Dual function low pressure cutout for refrigeration system

ABSTRACT

A single low pressure cutout is provided in a control arrangement to provide normal low pressure protection during a cooling demand, and to shutdown the compressor after a pumpdown operation. The arrangement includes a lockout circuit and switch means which function to switch the low pressure cutout into the lockout circuit for normal low pressure protection, and out of it for the pumpdown operation.

United States Patent 1 91 Stewart Mar. 12, 1974 [5 DUAL FUNCTION LOW PRESSURE 3,171,264 3/1965 Griffin 62/209 3,563,048 2/1971 Barry 62/209 CUTOUT FOR REFRIGERATION SYSTEM [58] Field Inventor:

Assignee:

Filed:

Appl. No.: 345,158

Robert S. Stewart, Staunton, Va.

Westinghouse Electric Corporation, Pittsburgh, Pa.

Mar. 26, 1973 US. Cl 62/203, 62/209, 62/227,

Int. Cl. F25b 41/00 of Search 62/203, 204, 208, 209, 62/226, 227, 228, 229

References Cited UNITED STATES PATENTS 6/1963 Liehrecht .l. 62/226 Primary ExaminerMeyer Perlin Attorney, Agent, or FirmE. C. Arenz [57] ABSTRACT A single low pressure cutout is provided in a control arrangement to provide normal low pressure protection during a cooling demand, and to shutdown the compressor after a pumpdown operation. The arrangement includes a lockout circuit and I switch means 'which function to switch the low pressure cutout into the lockout circuit for normal low pressure protection, and out of it for the pumpdown operation.

6 Claims, 2 Drawing Figures PATENIEDMAR 12 614 FIG. I.

p 26 l l l EE S fiZZZ ri U FIG. 2.

DUAL FUNCTION LOW PRESSURE CUTOUT FOR REFRIGERATION SYSTEM BACKGROUND OF THE INVENTION conventionally used arrangements to obtain the two functions which my invention provide is considered apropos.

Normal low pressure protection of refrigeration systerns of the type with which my invention is concerned is desired when the suction line pressure goes below a predetermined setting while a cooling demand exists, the low pressure typically being caused by some fault such as low refrigerant charge, or dirty evaporator filters, or low evaporator air flow, or indoor fan failure, for example. Such refrigeration system conditions may well result in icing of the evaporator and may result in equipment failure, or at the least unsatisfactory cooling, if permitted to continue. Hence, the low pressure cutout device used for normal low pressure protection is usually provided in a lockout circuit, that is, a circuit which requires a manual reset, if the circuit is energized.

As is well known, the purpose of a compressor pumpdown after the cooling demand is satisfied is to permit the compressor to clear itself of refrigerant before shutdown, and thereby preventing slugging on startup. This is conventionally done by closing the liquid line to the evaporator with a solenoid operated valve. The compressor continues to operate after the valve is closed until a predetermined low pressure is sensed by a low pressure cutout device which stops compressor operation. Since a pumpdown occurs on every cycle of the cooling demand thermostat, it requires a low pressure cutout device that automatically resets. A preferred setting for the. low pressure cutout devices for both functions is, in my view, about 30 psig.

So far as I know, the conventional way to obtain the normal low pressure protection, while also permitting a pumpdown, is to use two different low pressure cut out devices, with one being arranged to provide a lockout if the low pressure occurs, and the other one resetting automatically. This also requires of course that the cutout device for normal low pressure protection be set at a substantially lower value, such as 5 psig compared to 30 psig, so as not to interfere with the pumpdown function. Since the setting of 5 psig on the normal low pressure protection will not protect against icing of the evaporator, typically an additional device such as a refrigerant thermostat associated with the evaporator coil is used to sense extreme cold conditions for stoppong the compressor. With this arrangement, the cutout device used for the normal low pressure protection isin fact only protecting for a loss of refrigerant charge.

SUMMARY OF THE INVENTION In accordance with my invention, a single low pressure cutout device is provided in a control arrangement including a manually resettable circuit breaker in a lockout circuit, and switching means is provided to switch the low pressure cutout device into the lockout circuit for normal low pressure protection and out of I the lockout circuit for the pumpdown operation. In my currently preferred operation, the lockout circuit includes one parallel branch including the tripping coil of the circuit breaker and another parallel branch including overload switch means, both of the parallel branches being in series with the circuit breaking contacts of the circuit breaker. The lockout circuit changing switch means is operable in accordance with operation of the cooling demand thermostat to connect the switch means of the low pressure cutout device in the parallel branch including the overload switch means in response to a demand for cooling so that a suction pressure below a given level will actuate the circuit breaker by energizing the tripping coil, and to connect the switch means of the low pressure cutout device in series with the other parallel branch in response to satisfaction of the cooling demand thermostat so that termination of compressor operation can occur following pumpdown without actuating the circuit breaker when the switch means of the low pressure cutout device operate to an open position.

DRAWING DESCRIPTION DESCRIPTION OF THE PREFERRED EMBODIMENT I The diagrammatically represented refrigeration system of FIG. 1 includes a compressor 10, condenser 12, evaporator 14 and fan 16 therefor and the connecting lines therebetween which include expansion valve 18 and suction line valve 20 therein as shown. Valve 20 is operated by solenoid 22 to a closed position at the appropriate time to provide for a pumpdown operation.

The low pressure cutout device includes a switch 24 operable in accordance with the suction pressure sensed in the suction line downstream from the suction valve 20, by the suction pressure sensing means designated 26.

In the arrangement of FIG. 2, opposite sides of a voltage source areindi'cated by lines L1 and L2. For purposes of explaining the invention, 28 indicates the compressor motor although it will be understood that for refrigeration systems of the larger sizes 28 can be indicative of the coil of a motor contactor for controlling the energization of a motor energized from a different voltage source. In that same connection, a transformer 30 is shown for stepping down .the voltage for the major part of the control circuit. To energize the compressor motor, switch 32 must be closed by the cooling control relay coil 34. I

Referring to FIG. 2, the other major parts of the control arrangement will now be described. The cooling demand thermostat including its switch 36 is open when satisfied and closes when cooling is demanded. The circuit breaker generally designated 38 is of the manual reset type and includes a tripping coil 40 and the breaking contacts 42, and is normally closed. A first control relay is provided which includes a coil 44 controlling normally open switch 46, normally open switch 48, and normally closed switch 50. A second control relay is provided which includes coil 52 and normally open switches 54 and 56. The circuit alsoincludes switches 58 and 60 which are normally closed overload switches operated to open positions in response to one or another abnormal operating conditions as sensed by the devices carrying the legendsOL-l and OL-2.

For purposes of description of this invention, the lockout circuit portion of the control arrangement includes the breaker contact switch 42 in series with one branch parallel circuit including the tripping coil 40, and anotherbranch parallel circuit including the overload switches 58 and 60. The low pressure cutout device switch 24 is connected in parallel with the tripping coil during normal cooling operation to provide a low suction pressure shutdown if such condition arises, and is connected in series with the two parallel branches of the lockout circuit to preclude tripping the circuit breaker during a pumpdown operation preceding com- A pressor shutdown, which is then effected by opening of the cutoutdevice switch 24.

The switches controlled by the first control relay coil 44 perform the following functions. Switch 46 serves to complete part of the control circuit to permit initially energizing the compressor when the cutout device switch 24 closes during a normal startup. Switch 48 completes part of the one parallel branch of the lockout circuit after the cutout device switch 24 has closed during the normal startup. Switch 50 serves to connect the cutout device switch 24 in series with the two parallel branches of the lockout circuit when switch 50 is closed, and to isolate it from the one branch including the tripping coil 40 when it is opened.

The function of the switches of the second control relay controlled by coil 52 are as follows. Switch 56 completes what can be considered to be a holding circuit which permits continued compressor operation after a cooling demand has been satisfied and the pumpdown is occurring. Switch 54, by remaining open during normal startup before the cutout device switch 24 closes, prevents the circuit breaker from tripping through the circuit which would be completed through switch 54 if closed at that time. However, switch 54 must close after the cutout device switch 24 closes to provide a complete branch circuit with the tripping coil 40.

OPERATION After a normal cooling operation and compressor shutdown following a suction pumpdown, the thermostat 36 is open, the coil 44 of the first control relay is deenergized, the suction line valve 20 is closed by its controlling solenoid 22 being deenergized, and the cutout device switch 24 is open in response to the pressure in the suction line being below the established pressure setting.

When cooling is demanded, the thermostat 36 closes, the coil 44 of the first control relay is energized so that its controlled switches 46 and 48 close and 50 opens, and the suction line valve 20 is opened by the energization of its solenoid 22. Opening of the suction line valve 20 will relieve the low pressure in the suction line downstream of the valve 20, if such a low pressure exists at that time, and the cutout device switch 24 will close. Thus a compressor energizing control circuit is established through the first control relay switch 46, the closed circuit breaker breaking contacts 42, the overload switches 58 and 60, and the cutout device switch 24. This results in energization of the cooling relay coil 34 and closure of its controlled switch 32 to complete the circuit in which the compressor motor, or operating coil 28 for a motor contactor, is located. Before thecutout device switch 24 closes, energization of the circuit breaker tripping coil is prevented by switch 54 of the second control relay being open until the switch 24 closes.

After the cutout device switch 24 closes, the cutout device switch and the overload switches 58 and 60 are in a parallel circuit with the tripping coil 40 of the circuit breaker so that if any overload condition, or a low pressure condition in the suction line arises, causing any of these switches to open, the circuit breaker will be tripped by energization of its tripping coil. The parallel circuit in which the tripping coil is connected is established by the closure of the switch 54 of the second control relay following closure of the cutout device switch 24, the earlier closed switch 48 of the first control relay, and the earlier opened switch 50 of the first control relay.

After the thermostat is satisfied so that its switch-36 opens, the first control relay is deenergized so that its control switches 46, 48, and 50 take the positions shown in FIG. 2, the suction line valve 20.is closed by deenergization of its solenoid 22, and the cutout device I switch 24 remains closed until a suction pressure below the setting is detected by the suction pressure sensor 26. By closing of the switch 50 of the first control relay, the cutout device switch 24 is now in series with the one branch including the overload switches 58 and 60, and the other branch including the tripping coil 40. Accordingly, the switch 24 is effectively outside the lock- I out circuit.

While the pumpdown operation occurs, the compressor remains energizedthrough a completed control circuit including switch 56 of the second control relay, the circuit breaking contacts 42, the two overload switches 58 and 60, and the cutout device switch 24 which cornpletes the circuit to both the second control relay coil 52 and the parallel cooling relay coil 34. After the pumpdown has reduced the suction line pressure downstream from the valve 20 to below the setting of the cutout device, the switch 24 opens and the circuit is as it was first stated above following a normal cooling operation and shutdown.

It is noted that should any abnormalcondition arise causing opening of either of the overload switches 58 or 60 during a pumpdown, the circuit breaker will be tripped to a position requiring manual reset.

It is considered that oneof the salient advantages of the arrangement is that the suction line pressure setting breaker requiring manual reset during a normal pumpdown.

I claim:

1. In a control arrangement for a refrigeration system having a valve to permit a compressor pumpdown operation following satisfaction of cooling demand as sensed by a thermostat:

a manually resettable circuit breaker including normally closed breaking contacts and a tripping coil;

a circuit including one parallel branch in'which said tripping coil is connected, and another parallel branch, said parallel branches being in series with said breaker contacts;

a cutout switch operable to an open and a closed position in response to suction line pressures respectively below and above an established setting; and

switch means for connecting said cutout switch in said another parallel branch to effect tripping of said breaker by energization of said tripping coil upon opening of said cutout switch while a cooling demand exists, and for connecting said cutout switch in series with said parallel branches upon satisfaction of said cooling demand to prevent tripping of said breaker while said compressor pumpdown operation occurs and until said cutout switch opens in response to completion of said pumpdown.

2. In a control arrangement for a refrigeration system having a valve to permit a compressor pumpdown operation following satisfaction of cooling demand as sensed by a thermostat:

a manually resettable circuit breaker including normallyclosed breaking contacts and a tripping coil; a cutout switch operable to. an open and a closed position in response to suction line pressures respectively below and above an established setting;

switch means for. connecting said cutout switch in parallel with said tripping coil while the cooling demand exists so that energization of said tripping coil will occur while said cooling demand exists upon opening of said cutout switch, and for connecting said cutout switch in series with both saidtripping coil and a circuit in parallel with said tripping coil upon satisfaction of a cooling demand so that energization of said tripping coil is avoided when said cutout switch opens following compressor pumpdown.

3. In a control arrangement for a refrigeration system including a compressor, condenser, evaporator, connecting lines therebetween, a thermostat, and a valve for restricting refrigerant flow to said compressor following satisfaction of a cooling demand sensed by said thermostat:

a manually resettable circuit breaker having normally closed circuit breaking contacts and a tripping coil;

a low pressure cutout switch responsive to suction pressure downstream from said valve, said cutout switch being connected in series with relay means controlling energization of said compressor;

a circuit having one parallel branch including said tripping coil, and another parallel branch, said parallel branches being connected in series with said circuit breaker contacts; and

switch means operable in accordance with operation of said cooling demand thermostat for connecting said cutout switch means in said another parallel branch in response to a demand for cooling, so that opening of said cutout switch in response to a suction pressure below a given level will open said breaking contacts by energizing said tripping coil, and for connecting said cutout switch means in series with said parallel branches in response to satisfaction of said thermostat so that opening of said cutout switch and termination of compressor operation will occur following pumpdown without opening said circuit breaking contacts.

4. In a control arrangement according to claim 3 including:

a solenoid for opening said suction line valve when energized;

a relay coil for operating said switch means;

said solenoid and said relay coil are connected in parallel with each other and in series with said thermostat.

5. In a control arrangement according to claim 3 wherein:

said another parallel branch includes overload switch means.

6. A control arrangement for a refrigeration system including a compressor, condenser, evaporator, connecting lines therebetween, and a solenoid operated valvefor restricting refrigerant flow to said compressor, comprising:

a thermostat;

a control power source;

a manually resettable circuit breaker having normally closed circuit breaking contacts and a tripping coil;

a low pressure cutout switch responsive to suction line pressure downstream from said valve;

overload switch means;

a cooling relay including a coil and switch means for effecting energization of said compressor when said coil is energized;

a first control relay including a coil and first and second normally open switches and a third normally closed switch;

a second control relay including a coil and first and second normally open switches;

one circuit across said source including said thermostat connected in series with said solenoid and said first control relay coil in a first parallel circuit;

another circuit across said power source from one side thereof to the other, including;

a secondparallel circuit including in parallel said first switches ofsaid first and second control relays, said second parallel circuit being connected in series with said breaking contacts,

a third parallel circuit in series with said breaking contacts including, in series in one branch said tripping coil and said second switches of said first and second control relays, and in series in the other branch said overload switch means and said cutout switch,

a third parallel circuit in series with said second parallel circuit, said third parallel circuit including said second relay coil in parallel with said cooling relay coil, I

said third normally closed switch of'said first control relay being connected between the two branches of mostat results in connecting of said cutout switch in and out of parallel with said tripping coil so that said low pressure cutout switch provide normal low suction pressure protection while the cooling demand exists, while permitting a compressor pumpdown after a cooling demand is satisfied. 

1. In a control arrangement for a refrigeration system having a valve to permit a compressor pumpdown operation following satisfaction of cooling demand as sensed by a thermostat: a manually resettable circuit breaker including normally closed breaking contacts and a tripping coil; a circuit including one parallel branch in which said tripping coil is connected, and another parallel branch, said parallel branches being in series with said breaker contacts; a cutout switch operable to an open and a closed position in response to suction line pressures respectively below and above an established setting; and switch means for connecting said cutout switch in said another parallel branch to effect tripping of said breaker by energization of said tripping coil upon opening of said cutout switch while a cooling demand exists, and for connecting said cutout switch in series with said parallel branches upon satisfaction of said cooling demand to prevent tripping of said breaker while said compressor pumpdown operation occurs and until said cutout switch opens in response to completion of said pumpdown.
 2. In a control arrangement for a refrigeration system having a valve to permit a compressor pumpdown operation following satisfaction of cooling demand as sensed by a thermostat: a manually resettable circuit breaker including normally closed breaking contacts and a tripping coil; a cutout switch operable to an open and a closed position in response to suction line pressures respectively below and above an established setting; and switch means for connecting said cutout switch in parallel with said tripping coil while the cooling demand exists so that energization of said tripping coil will occur while said cooling demand exists upon opening of said cutout switch, and for connecting said cutout switch In series with both said tripping coil and a circuit in parallel with said tripping coil upon satisfaction of a cooling demand so that energization of said tripping coil is avoided when said cutout switch opens following compressor pumpdown.
 3. In a control arrangement for a refrigeration system including a compressor, condenser, evaporator, connecting lines therebetween, a thermostat, and a valve for restricting refrigerant flow to said compressor following satisfaction of a cooling demand sensed by said thermostat: a manually resettable circuit breaker having normally closed circuit breaking contacts and a tripping coil; a low pressure cutout switch responsive to suction pressure downstream from said valve, said cutout switch being connected in series with relay means controlling energization of said compressor; a circuit having one parallel branch including said tripping coil, and another parallel branch, said parallel branches being connected in series with said circuit breaker contacts; and switch means operable in accordance with operation of said cooling demand thermostat for connecting said cutout switch means in said another parallel branch in response to a demand for cooling, so that opening of said cutout switch in response to a suction pressure below a given level will open said breaking contacts by energizing said tripping coil, and for connecting said cutout switch means in series with said parallel branches in response to satisfaction of said thermostat so that opening of said cutout switch and termination of compressor operation will occur following pumpdown without opening said circuit breaking contacts.
 4. In a control arrangement according to claim 3 including: a solenoid for opening said suction line valve when energized; a relay coil for operating said switch means; said solenoid and said relay coil are connected in parallel with each other and in series with said thermostat.
 5. In a control arrangement according to claim 3 wherein: said another parallel branch includes overload switch means.
 6. A control arrangement for a refrigeration system including a compressor, condenser, evaporator, connecting lines therebetween, and a solenoid operated valve for restricting refrigerant flow to said compressor, comprising: a thermostat; a control power source; a manually resettable circuit breaker having normally closed circuit breaking contacts and a tripping coil; a low pressure cutout switch responsive to suction line pressure downstream from said valve; overload switch means; a cooling relay including a coil and switch means for effecting energization of said compressor when said coil is energized; a first control relay including a coil and first and second normally open switches and a third normally closed switch; a second control relay including a coil and first and second normally open switches; one circuit across said source including said thermostat connected in series with said solenoid and said first control relay coil in a first parallel circuit; another circuit across said power source from one side thereof to the other, including; a second parallel circuit including in parallel said first switches of said first and second control relays, said second parallel circuit being connected in series with said breaking contacts, a third parallel circuit in series with said breaking contacts including, in series in one branch said tripping coil and said second switches of said first and second control relays, and in series in the other branch said overload switch means and said cutout switch, a third parallel circuit in series with said second parallel circuit, said third parallel circuit including said second relay coil in parallel with said cooling relay coil, said third normally closed switch of said first control relay being connected between the two branches of said third parallel circuit, with one side of said third switch being conneCted between said overload switch means and said cutout switch, and the other side of said third switch being connected between said tripping coil and said second switch of said first control relay; whereby energization of said first control relay coil in accordance with closing and opening of said thermostat results in connecting of said cutout switch in and out of parallel with said tripping coil so that said low pressure cutout switch provide normal low suction pressure protection while the cooling demand exists, while permitting a compressor pumpdown after a cooling demand is satisfied. 